I've owned both. Well, 2011 WRX and 2010 MS3, but I don't believe there were any changes in the Mazda for 2011.
The WRX is much quicker off the line and through 2nd. But when the Mazda hits full boost in 3rd, watch out.
The MS3 pulls very strong in gears 3-5.
I'm sure any track test numbers you find online will back that up.